From the scheduled six days of shooting to take place at Pompeii, three days were lost trying to get enough electric power to the amphitheater, as the equipment demanded too much from the local electric installation. In the end, a cable had to run from the center of Pompeii to the amphitheater.
Only the songs "Echoes pt. 1 and 2", "A Saucerful of Secrets" and "One of These Days" were actually filmed in Pompeii. The songs "Careful With That Axe Eugene", "Set the Controls For the Heart of the Sun", and "Mademoiselle Nobs" were actually filmed in a studio in Paris, where extra shooting took place for the blue-screen shots in the Pompeii performances. This explains the extra lighting rig and disappearance of Richard Wright's beard in the Paris-shot songs.
During "One of These Days" the film is primarily of Nick Mason's manic drumming. Much more was filmed of the rest of the band, particularly David Gilmour's slide guitar, but all except the tapes of Mason were lost.
At the start of Echoes Part 1, you can hear three piano parts being played and once one part stops, Roger Waters is seen to move away from the Piano and set up his bass. This shows that Roger Waters was in fact playing the keyboard part.